Not Applicable
The invention relates generally to roller bearings, and more particularly to retainerless precessing roller bearings for use in rotary or oscillatory applications, such as for supporting rotating or oscillating shafts.
Known roller bearings include various means for guiding and positioning rollers. For example, self-aligning angular contact roller bearings are shown in U.S. Pat. No. 2,387,962 issued Oct. 30, 1945 and U.S. Pat. No. 2,767,037 issued Oct. 16, 1956. In each of those patents, the illustrated roller bearing includes an inner ring that provides a substantially spherical inner race surface, a pair of outer race surfaces having convex curvatures, and a pair of oppositely inclined rows of symmetrical hourglass-shaped rollers. Those roller bearings also include bearing cages or retainers to separate, guide and position the rollers in each row. An example of the above-described roller bearing is produced by Rexnord Corporation, Bearing Operation, Downers Grove, Ill., and has a Model No. DAS4-14A.
Japanese Patent No. 60-188617 illustrates a roller bearing having opposite rows of asymmetrical rollers and a center guide ring. The shape of the rollers and the center guide ring operate to guide and position the rollers in each row.
It is also known to provide integral collars or shoulders on the inner ring or the outer ring of a roller bearing to guide the rollers. An example of such a roller bearing is illustrated in U.S. Pat. No. 3,912,346 issued Oct. 14, 1975. In that roller bearing, an inner ring is provided with radially extending integral collars between which the rollers are confined.
The loads exerted on a bearing unit such as those described above are typically carried by the rollers in only one part of the unit at a time, that part being referred to as the xe2x80x9cload zone.xe2x80x9d Especially where bearings are used in oscillatory applications, such as in aircraft flight control surfaces, it is desired that the rollers precess or index so that they are all cycled through the load zone. Cycling the rollers results in utilization of the entire race surface of each of the rollers to extend rolling contact fatigue life. Cycling the rollers also redistributes grease for improved lubrication of the bearing unit which in turn reduces fretting damage and improves the bearing unit""s resistance to raceway corrosion. To cause such precessing or indexing of the rollers, it is known to use a retainer with skewed pockets. A known retainer has fingers or prongs inclined slightly to provide an imbalanced amount of skew to the rollers which causes the rollers to precess or index during oscillation of the bearing.
A disadvantage associated with the foregoing roller bearing units is the inclusion of a bearing cage, retainer, guide ring, integral collar, or the like. Such components are costly to produce and assemble as part of the bearing unit. Those components also occupy space within the bearing unit that could otherwise be used for additional rollers and/or additional lubricant.
A full complement self-aligning roller bearing without a retainer guide ring is disclosed in U.S. Pat. No. 5,441,351 and assigned to the assignee of the invention disclosed herein. Although the bearing disclosed in the ""351 patent provides some skew control of the bearings, roller precession is less consistent than can be achieved with the use of a retainer having skewed pockets. Therefore, a need exists for a retainerless roller bearing having consistent roller precessing.
The invention provides an improved retainerless roller bearing apparatus particularly suited for oscillatory service. Applicant has discovered that, surprisingly, consistent precessing in a bearing can be achieved in a retainerless roller bearing apparatus including axially inclined rollers disposed between inner and outer race surfaces by maintaining a radial internal clearance of no more than 0.002 inches between each roller and the inner and outer race surfaces. The races having the specified roller clearance controls the skew of the rollers to consistently precess the rollers in an oscillatory operation.
Applicant has observed that the bearing apparatus embodying the invention precesses or indexes to cycle the rollers through the load zone. The observed roller precession was greater (i.e., more consistent) than can be achieved with the use of a retainerless bearing, such as disclosed in U.S. Pat. No. 5,441,351.
In particular, the invention provides a retainerless bearing apparatus including an inner ring member having an arcuate inner race surface, an outer ring member having an arcuate outer race surface, and a row of rollers in the raceway space defined between the inner and outer race surfaces with a radial internal clearance of no more than 0.002 inches between each roller and the race surfaces.
In one embodiment, the retainerless bearing apparatus includes an inner race member having a spheroidal inner race surface, and an outer race member having a convex outer race surface opposing the inner race surface. The bearing apparatus also includes a plurality of rollers arranged in a row in the raceway space between the inner and outer race surfaces with a radial internal clearance of no more than 0.002 inches between the rollers and the race surfaces. Each of the rollers includes a concave longitudinal profile (i.e., is hourglass-shaped) having a radius of curvature that is somewhat greater than the radius of curvature of each of the convex outer race surface and the spheroidal inner race surface. Applicant has discovered that this relationship between the rollers and the race surfaces provides roller skew control for the bearing to consistently precess without a retainer, guide ring, collar, or other means apart from the primary race surfaces for holding, positioning or guiding the rollers.
This and still other objects and advantages of the present invention will be apparent from the description which follows. In the detailed description below, preferred embodiments of the invention will be described in reference to the accompanying drawings. These embodiments do not represent the fall scope of the invention. Rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention.